Jaeho Shim

Partially directional microdisk laser with two Rayleigh scatterers

We report a partially directional microdisk semiconductor laser with subwavelength-scale boundary perturbations for asymmetric backscattering of counterpropagating whispering gallery modes. Unlike the previous approaches based on optical bistability, the directionality and chirality of the laser modes can be fine-tuned and partially controlled by adjusting the dimension, shape, and relative positions of Rayleigh scatterers on the microdisk perimeter. The controlled directionality is investigated using numerical simulations and experiments for wavelength-scale microdisk resonators with an azimuthal mode number of 5.

Fluorescence detection system with miniaturized integrating sphere

We report on the use of non-imaging reflectors to improve the collection efficiency of fluorescence detection systems. Half-sphere mirrors redirect the isotropic fluorescent emission toward the photodetector, and significantly enhance the fluorescence signal.

Hybrid integration of III-V semiconductor lasers on silicon waveguides using optofluidic microbubble manipulation.

Optofluidic manipulation mechanisms have been successfully applied to micro/nano-scale assembly and handling applications in biophysics, electronics, and photonics. Here, we extend the laser-based optofluidic microbubble manipulation technique to achieve hybrid integration of compound semiconductor microdisk lasers on the silicon photonic circuit platform. The microscale compound semiconductor block trapped on the microbubble surface can be precisely assembled on a desired position using photothermocapillary convective flows induced by focused laser beam illumination. Strong light absorption within the micro-scale compound semiconductor object allows real-time and on-demand microbubble generation. After the assembly process, we verify that electromagnetic radiation from the optically-pumped InGaAsP microdisk laser can be efficiently coupled to the single-mode silicon waveguide through vertical evanescent coupling. Our simple and accurate microbubble-based manipulation technique may provide a new pathway for realizing high precision fluidic assembly schemes for heterogeneously integrated photonic/electronic platforms as well as microelectromechanical systems.

Randomly Distributed Fabry-Pérot-type Metal Nanowire Resonators and Their Lasing Action

Optical feedback mechanisms are often obtained from well-defined resonator structures fabricated by top-down processes. Here, we demonstrate that two-dimensional networks of metallic nanowires dispersed on the semiconductor slab can provide strong in-plane optical feedback and, thus, form randomly-distributed Fabry-Pérot-type resonators that can achieve multi- or single-mode lasing action in the near infrared wavelengths. Albeit with their subwavelength-scale cross-sections and uncontrolled inter-nanowire distances, a cluster of nearly parallel metal nanowires acts as an effective in-situ reflector for the semiconductor-metal slab waveguide modes for coherent optical feedback in the lateral direction. Fabry-Pérot type resonance can be readily developed by a pair of such clusters coincidentally formed in the solution-processed random nanowire network. Our low-cost and large-area approach for opportunistic random cavity formation would open a new pathway for integrated planar light sources for low-coherence imaging and sensing applications.

Lasing in hybrid metal-Bragg nanocavities

We report room-temperature lasing from an optically pumped subwavelength-scale cylindrical InGaAsP pillar surrounded by circular Bragg reflectors on a metal substrate with a dielectric spacer layer. By taking advantage of wide in-plane photonic bandgaps and proper vertical antiresonances, three dielectric Bragg pairs produce a sufficient optical feedback capable of low threshold lasing from the fundamental TE011 mode. A large spontaneous emission coupling into the lasing mode is obtained from the cavity-enhanced Purcell effects and effective suppression of nonlasing modes.

Hydrothermal fabrication of patterned ZnO nanorod clusters using laser direct writing

We report on the hydrothermal synthesis of ZnO nanorod clusters by localized optical heating from the focused laser beam. The spatial distribution of the nanorods and their growth rate can be easily controlled.

Nano pillar array laser with a bottom metal plane

We report a photonic bandedge laser using subwavelength-scale pillars with a metal reflector plane bonded on the silicon substrate. Surface-emitting operation near the gamma point of the photonic band diagram is observed at 77 K.

Optically pumped subwavelength-scale metallodielectric nanopatch resonators

We discuss subwavelength-scale semiconductor metal-optic resonators placed on the metal substrate with various top metal plate sizes. Albeit with large optical losses, addition of metal layers converts a leaky semiconductor nano-block into a highly-confined optical cavity. Optically pumped lasing action is observed with the extended top metal layer that can significantly suppress the radiation losses. Careful investigation of self-heating effects during the optical carrier injection process shows the importance of temperature-dependent material properties in the laser rate equation model and the overall laser performances.

Photothermal in-situ synthesis of localized tungsten oxide nanobeam structures

We demonstrate tungsten oxide semiconductor nanostructures fabricated by photothermal oxidation processes on the suspended metal nano-layer. The electrical conductivities of the nanobeam structures are measured against the temperature to validate their metal/semiconductor material properties.

Nanopatch cavity with a subwavelength-scale cuboidal semiconductor core

We propose a modified nanopatch cavity with a cuboidal semiconductor sandwiched between extended metal planes. Experimental results show the quality factor of ~200 can be achieved with an effective mode volume of ~0.0064 cubic wavelength.